1. Field of the Invention
The present invention relates to an airbag device, and more particularly to an airbag device including a tether formed in such a manner that the expansion length of the middle part of an airbag is shorter than the expansion length of both side edges of the airbag when the airbag is expanded.
2. Description of the Related Art
As shown in FIGS. 1 and 2, a conventional airbag device for vehicles generally comprises: an airbag housing 2 mounted to an instrument panel; an airbag 4 accommodated in the front part of the airbag housing 2; an inflator 6 mounted to the rear of the airbag housing 2 for supplying a high-pressure gas to the airbag 4 so that the airbag 4 is expanded toward a passenger 10 when a collision occurs; and an impact sensor (not shown) for sensing a collision of a vehicle.
In the conventional airbag device with the above-stated construction, the high-pressure gas is supplied from the inflator 6 to the airbag 4 when a collision is sensed by means of the impact sensor. As the gas is filled in the airbag 4, the airbag 4 passes through the instrument panel and is expanded toward the passenger 10, as indicated by a dotted line in FIG. 1 and by a solid line in FIG. 2, to absorb kinetic energy from the passenger 10 and thus protect the passenger 10 from injury.
To the inside of the airbag 4 is sewn a tether 8, made of a textile fabric, by which the expansion length of the airbag 4 is determined.
In the conventional airbag device, however, a contact surface 4a of the airbag 4, which makes contact with the passenger 10, is flat. Consequently, the chest (if the passenger 10 is relatively tall) or the head (if the passenger 10 is relatively short) of the passenger 10 rapidly forced forward when the airbag 4 is expanded may be injured by the airbag 4 expanding toward the passenger 10 as shown in FIG. 2. Otherwise, the passenger 10 may be squeezed between the airbag 4 and a seat back 11 so that the passenger 10 may be killed. Furthermore, the passenger 10 may slip laterally from the contact surface 4a of the airbag 4 when a vehicle is rocked from side to side after the airbag has been expanded, whereby the passenger 10 is out of the protection range of the airbag 4.
In addition, the conventional airbag device has another problem in that the gas supplied from the inflator 6 is concentrated to the central region of the airbag 4, as indicated by a dotted line in FIG. 2, when the expansion of the airbag 4 is initiated, and therefore the central region of the airbag 4 is rapidly expanded, which causes a punch-out-force phenomenon hitting the passenger 10.